It is known that a rudder assembly of an aircraft comprises a fixed vertical stabilizer and a movable rudder. This rudder is connected to the fixed vertical stabilizer by articulation means which form an articulation axis and it can rotate about the latter when acted upon by actuating means, such as jacks. It is furthermore known that such a rudder comprises two lateral aerodynamic surfaces which meet at the rear end of the aircraft in order to form the trailing edge of the movable rudder, which is also that of the rudder assembly.
As the functioning of the said rudder progresses, wear phenomena increase the normal operational mechanical plays provided in the construction of the said articulation means and/or in the transmission means between the said actuating means and the said rudder.
In normal flight of the aircraft, that is to say with zero sideslip, the said rudder is positioned in the aerodynamic extension of the fixed vertical stabilizer, in alignment with the latter, and is subjected to practically no aerodynamic effects. However, because of increased plays due to wear, it can happen that, despite the virtual non-existence of aerodynamic forces applied to it, the rudder starts to vibrate under the effect of turbulence or normal instabilities of the aerodynamic airflow.
As the mechanical plays increase with the ageing of the said articulation means and of the said transmission means, the same applies to the amplitude of the vibration of the said rudder. Such vibration, even of large amplitude, is not prejudicial to the safety of the aircraft, but it generates irritation for the passengers, who feel vibration induced in the cabin, and piloting discomfort for the pilot or pilots.
When this vibration reaches an unacceptable amplitude with regard to the comfort of the passengers and the pilots, it is necessary to replace the wearing parts of the said articulation means and/or of the said transmission means, in order to return to the slight operational plays. Such a replacement operation is relatively complex and in practice it necessitates an immobilization of the aircraft, the duration of which is not generally compatible with that of stopovers.
It is of course possible to carry out preventive maintenance operations by replacing the said wearing parts before the amplitude of the vibration becomes a nuisance. Such preventive maintenance operations can be carried out during the aircraft's programmed maintenance periods but it then becomes routine to carry out interventions and replacements of parts which are not strictly necessary.